The problem is probably that the resolution used for the D600 doesn't fit the monitor. The D600 comes in 1400x1050 or 1024x768 displays. I don't know what that monitor can do, but when I used the 1400x1050 mode on a 1024x768 monitor, I had similar experiences with clipping. The solution is to reduce the resolution on the laptop first before activating the external display. Both KDE and Gnome have easy tools to do this reduction.